This invention relates to a brazing method for closing holes and, more particularly, to a brazing method and alloy for closing high pressure turbine blade tip cap holes to maximize filling of the holes, minimize porosity, improve oxidation resistance, and improve reliability.
During the manufacture of high pressure turbine blades of the type as shown in U.S. Pat. No. 5,232,343, tip cap holes are formed to locate casting cores. It is important to securely close such holes because otherwise cooling air leaks out of the tip rather than being directed over airfoil surfaces. The tip cap holes have a diameter on the order of 0.04 to 0.05 inch (about 0.1 cm to 0.13 cm). Heretofore such holes have been filled by injection with a 50% dense slurry of a fill alloy consisting of a relatively high melting point ("high melt") component (H1) (about 45 wt %) intermixed with a relatively low melting point ("low melt") component (L1) (about 55 wt %). The compositions of high melt and low melt components employed in prior practice are as follows:
High Melt Comp. (H1) Low Melt Comp. (L1) C 0.15-0.19 wt % C 0.05 max wt % Cr 13.7-14.3 Cr 14.8-15.8 Co 9.0-10.0 Co 9.5-11.0 Ti 4.8-5.2 Ta 3.0-3.8 Al 2.8-3.2 Al 3.2-3.7 W 3.7-4.3 B 2.1-2.5 Mo 3.7-4.3 Ni Balance W + Mo 7.7 min Plus incidental Ni Balance impurities Plus incidental impurities
During brazing the low melt component particles melt to a liquid and, upon solidification, densify and bond the high melt component particles in the tip cap hole. A disadvantage of this approach has been that the cooled filling has a high internal porosity level which results in susceptibility to oxidation in service, and that a lack of fill condition exists due to a meniscus-type void that has formed upon cooling.